Temperature indicator switch



F eb. 8, 1966 R. A. JOHNSON ETAL 3,234,350

TEMPERATURE INDICATOR SWITCH Filed Feb. 11, 1964 FIG. 3

FIG. 2

INVENTOR. ROBERT A. JOHNSON BY PETER M. BYAM ATT NEY United States Patent 3,234,350 TEMPERATURE INDICATOR SWITCH Robert A. Johnson and Peter M. Byam, Greece, N.Y., assignors to Fasco Industries, Inc., Rochester, N.Y., a corporation of New York Filed Feb. 11, 1964, Ser. No. 344,041 8 Claims. (Cl. 200-138) This invention relates to a heat-responsive switch and more particularly to a temperature indicating switch for sensing and indicating either a single-temperature or two ditferent temperatures. In a more specific aspect, the invention relates to a switch of this character which may be used in an electrical circuit to light a bulb or bulbs, or to operate a small appliance such as a relay, buzzer, etc.

One object of the invention is the provision of a novel heat-responsive, electrical switch including a fixed contact arrangement whereby only a quick an dsimple adjustment is required for calibration after assembly.

Another object is to provide a switch of this type which is of extremely compact and rugged construction, includes only a very small number of parts, and is relatively simple and inexpensive to manufacture, yet which may be quickly and accurately calibrated.

The foregoing and other objects and advantages of the invention will be apparent from the following detailed description of a representative embodiment thereof, and from the recital of the appended claims particularly when taken in conjunction with the drawing, wherein:

FIG. 1 is a plan View of a temperature-indicator switch made according to the presently preferred embodiment of the invention, showing the switch as it appears when ready for calibration;

FIG. 2 is a side elevation, partly broken away, of this switch;

FIG. 3 is a fragmentary, cross-sectional view on an enlarged scale of the switch shown in FIGS. 1 and 2, showing how the switch is sealed after it is calibrated; and

FIG. 4 is a bottom view on an enlarged scale of the closure member of the switch, showing the closure member'a'pa-rt from the switch housing.

In the illustrated embodiment of the invention, the switch includes a cylindrical housing of a conductive material having an insulating closure at one end. A thermostatic switch element such as a bi-metal strip is mounted within the housing and fixed at one end to the housing. Its opposite end stands free adjacent to the closure for movement responsively to temperature changes. Two fixed contacts are carried by the closure for alternate engagement by the bimetallic element. The two fixed contacts consist of conductive strips running along opposite Walls of a spiral cam groove in the closure.- The free end of the bimetallic element extends into the groove and is movable across it -from one fixed contact to. the other.

In assembly, forcalibration, the switch is first brought to one of its design temperatures, that is, either the temperature at which the bimetallic element should engage the first fixed contact or the temperature at which it should engage the second fixed contact. The closure member is then rotated relative to the housing until the selected fixed contact is just engaged by the bimetallic element. The closure member is then cemented to the housing, or otherwise securely fixed against further rotation relative thereto so that the switch will remain permanently calibrated at the desired temperatures. The cam groove in the closure is of uniform width so that angular displacement of the closure changes only the operating temperatures of the switch and doesnot affect the temperature change required to cause the bimetallic element to move across the groove.

Referring now to the drawing, the switch shown therein includes a tubular housing 10, which may be formed 3,234,350 Patented Feb. 8, 1966 by extrusion, and is preferably of unitary construction. It has external threads 12 for mounting it in an internally threaded support (not shown); and it is hexagonally shaped, as denoted at 13, near its upper end for facilitating threading of it into its support. The lower end of the housing is closed by a unitary wall portion 14, which carries an integrally formed, inwardly extending embossment 16;. The upper side wall portion 18 of the housing is preferably made relatively thin to facilitate crimping it upon the closure member 20, which fits within the upper end of the housing and rests against an inwardly extending shoulder 22 therein. The housing provides the ground side of an electric circuit.

A bi-metallic strip 24 is fitted upon the embossment l6 and secured thereto. by staking. The strip 24 extends vertically from the bottom wall portion 14 of the housing, upwardly toward the closure member 20. At its upper end it has a contact wire 26 welded or otherwise secured to it. The closure member 20 may be molded from an insulating plastic and is formed on its under face with a spiral groove 28. *Fixed. conducting contacts 30 and 32 are secured to the bottom of the closure member 20 by rivets 34 and 36, which extend through the closure member and also secure external electrically-conductive terminals 38 and '39 to the closure member. The terminals 38 and 39 fit into notched embossment-s or terminal barriers 41 formed'on the upper surface of the closure member, integral therewith. Thereby the terminals 38 and 39 are securely positioned and held from rotating about their respective rivets 34 and 36.

The contacts 30 and 32 include upwardly extending flange portions 40 and 42, respectively, which extend into the groove 28 and conform to the lateral walls of the groove. The groove 28 is of uniform width throughout its length, and spirals outwardly about the center of the closure member 20 sufficiently to allow adjustment to be made for all manufacturing tolerances during calibration of the switch.

-In assembly, after the bi-metal element 24 is secured to the bottom wall portion 14 of the housing, the closure member 20, with the contacts 30 and 32 and the terminals 38 and 39 attached to it, is placed in the upper end of the housing 10. Tabs 44 struck from the upper wall portion 18 of the housing are then crimped lightly over the outer edge of the closure member 20 to retain the closure member in the housing, yet permit rotation of the closure member therein.

Preferably the bimetallic element is designed to move, when heated, toward the outside contact 32. The switch is calibrated by first soaking it for a brief time in a thermal medium held at a preselected temperature, the temperature at which the bimetallic element is intended to contact the outer fixed contact 42. The closure member 20 is then rotated relative to the housing until the contact wire 26 just engages this contact. The rotation of the closure member and its cam groove dimensionally changes the point of contact of the contact 32 with the bimetallic element. This allows the temperaure at point of contact to be controlled and adjusted.

The bimetallic element 24 and the contact 26 may be so positioned to either touch the inside cam contact 30 at normal room ambient (25 C.) and lose electrical contact at some temperature above room ambient, or they may be positioned to lose electrical contact at some temperature 'below normal room ambient. The inside cam contact 42 is so positioned, because of the uniform width of cam groove 28, that its dimensional relationship with outside contact 40 remains constant regardless of angular rotation of the closure 20 within the housing 10.

After calibration, the switch is sealed and the closure member 20 securely fixed in place by potting with an adhesive compound such as an epoxy resin 46 (FIG. 3),

which would account for 1 F. temperature change.

3 which is poured into the upper end of the housing upon the top of the closure member 20, and which provides an effective seal not only around the outer periphery of the closurev member 20 between it and the housing wall 18,

but also seals up the holes through which the rivets 34 and 36 extend,

calibration for both throws of the switch.

Because of this ability to calibrate for top and bottom indicating temperatures simultaneously, it is possible very easily and very quickly to calibrate a switch in the shop to suit the application and temperature limits for which it is intended to be used.

A typical example is a switch which is intended to allow a light bulb to remain lighted until the temperature of a device exceeds 100 F, and is intended'to light another bulb when the temperature exceeds 250 F. In this case the lateral spacing of contacts 40 and42 would have'to equal the distance the bimetallic element 24 woulddefiect while experiencing 150 F. temperature a differential plus the diameter of the contact 26. The ad- 'justa'ble dimensional change that can be achieved by rotation of the cam should be sufficient to compensate for all significant manufacturing tolerances. Dimensional variations must be compensated for by rotational adjustment of the cam. Therefore, the gain from one end of the cam groove to the other-must be great enough to compensate for all these variables, but also small enough to allow the largest possible mechanical advantage for adjustment. If we go back to the example cited above where there is a 150 F. differential (250 F.100 F.), and assume that the bimetal will deflect .001 inch for each 1 F. change in temperature, and that there is 300 of rotational adjustment available with the cam groove of the closure, the cam gains .100 inch from one end of the adjustment to the other. It can be seen then that rotating the closure for the whole 300 will cause a dimensional change between cam and contact of .100 inch which would also be equal to 100 F. Therefore the switch would have a'mechanical advantage which would allow 3 angularadjustment to equal .001 inch of movement If variables necessitated 150 F. of adjustment for 300 angular degrees of adjustment, then every two angular degrees of adjustment would equal .001 inch movement or 1' F. change in calibration. This latter situation is less desirable since it requires a higher degree of control of switch adjustment. Therefore it is an advantage to have the maximum number of angular degrees of adjustment result in the maximum required cam gain.

While the invention has been illustrated in connection with an embodiment in which there are two terminals 38 and 39, it might have only one terminal 38 or 39. When this single terminal is attached to the outside contact 32, the switch will act as a normally open switch. When the terminal is attached to the inside terminal 30, the switch will act as a normally closed switch. The switch might also be constructed with a single terminal but with that terminal bridging and riveted to both contacts 30 and 32. This last arrangement will provide an electrical circuit to ground at two different temperature ranges through a common terminal. In all these cases the switch is assumed to have a bimetallic element that deflects to the outside from its at rest position in contact with inside contact 30. However it should be understood that the switch may also be constructed so that the bimetallic element will deflect from the outside contact 32 to the inside contact 30.

While the invention has been described in connection with several different embodiments thereof, then, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the inventionor the limits of the appended claims.

Having thus described our invention, what we claim is:

1. A heat responsive electrical switch comprising (a) a housing of an electrically conductive material,

(b) an insulating member closing one end of said housing,

(c) a switch contact fixed to said member on the inwardly facing side thereof, said contact having a contact surface lying along a spiral around the center of said member in a plane transverse to the length of said housing, and I (d) a heat responsive conductive element mounted within saidhousing and electrically connected thereto for electrically connecting said housing to said switch contact during times when the ambient temperatue is beyond a predetermined value,

(c) said insulating member being rotatable relative to said housing after the switch is assembled thereby to facilitate rapid calibration of the switch.

2. A double throw heat responsive electrical switch comprising (a) a housing of an electrically conductive material,

(b) an insulating closure closing one end of said housing,

(c) two switch contacts fixed to said closure inwardly facing side thereof,

(d) said contacts having respective contact surfaces lying along respective parallel spirals around the center of said closure in a plane transverse to the length of said housing, and

(e) a heat responsive conductive member mounted within said housing and electrically connected thereto for electrically connecting said housing to one of. said contacts when the temperature of the switch exceeds one value and for connecting said hOusing to the other one of said contacts when the temperature of the switch falls below a second value,

(f) said closure being rotatable relative to said housing after the switch is assembled thereby to facilitate rapid-calibration of the switch. 7 a

'3. A double throw heat responsive electrical switch comprising (a) a housing of an electrically conductive material,

(b) an insulating closure closing one end of said housing,

(0) said closure having a groove in its inwardly facing surface, said groove being of uniform width and in spiral form extending around the center of said closure,

(d) a first contact fixed to said closure and having a contact surface lying along one edge of said groove,

(e) a second contact fixed to said closure and having a contact surface lying along the opposite edge of said groove, and

(f) a heat responsive conductive member fixed at one of its ends to said housing with its other end free and standing within said groove,

(g) said closure beingrotatable relative to said housing after the switch is assembled thereby to facilitate rapid calibration of the switch.

4. A double throw heat responsive electrical switch comprising (a) a housing of an electrically conductive material,

(b) an insulating closure closing one end of said housing,

(c) said closure having a groove in its inwardly facing surface, said groove being of uniform width and in on the spiral form extending around the center of said closure,

(d) a first contact fixed to said closure and having a contact surface lying along one edge of said groove,

(e) a second contact fixed to said closure and having a contact surface lying along the opposite edge of said groove,

(f) two terminals mounted on the outwardly facing surface of said closure,

(g) means electrically connecting said two terminals,

respectively, to said two contacts, and

(h) a heat responsive conductive member fixed at one of its ends to said housing with its other end free and standing within said groove,

(i) said closure being rotatable relative to said housing after the switch is assembled therby to facilitate rapid calibration of the switch.

5. A double throw heat responsive electrical switch comprising (a) a housing of an electrically conductive material,

(b) an insulating closure closing one end of said housing,

(c) said closure having a groove in its inwardly facing surface, said groove being of uniform width and in spiral form extending around the center of said closure,

(d) a first contact fixed to said closure and having a contact surface lying along one edge of said groove,

(e) a second contact fixed to said closure and having a contact surface lying along the opposite edge of said groove,

(f) a heat responsive conductive member fixed at one of its ends to said housing with its other end free and standing within said groove, and

(g) means for securely fixing said closure to said housing after the switch has been calibrated.

6. A heat-responsive electrical switch comprising (a) a housing having a wall portion closing one end thereof, said housing being ofan electrically con ductive material,

(b) an insulating member closing the end of said housing opposite from said one end, the inwardly 'facing wall of said insulating member having a radially facing surface arranged spirally about the center of said member,

(c) a conductive contact member extending along said surface,

(d) a terminal mounted on the outer surface of said insulating member,

(e) means electrically connecting said terminal to said contact, and

(f) a heat-responsive conductive element mounted within said housing and electrically connected thereto for establishing an electrical connection between said housing and said contact member during times when the ambient temperature is beyond a predetermined value,

(g) said closure being rotatable relative to said housing after the switch is assembled thereby to facilitate ra id calibration of the switch.

7. A heat-responsive electrical switch comprising (a) a housing made of an electrically conductive material,

(b) an insulating closure mounted on said housing to close one end of said housing,

(c) a pair of electrically-conductive contact members secured on the inside face of said closure both said contact members being arranged along spirals and extending spirally about a common center and being uniformly spaced apart from end to end,

(d) a bimetallic, heat-responsive element secured at one end within said housing and electrically connected thereto and having its other end disposed for movement between said contact members,

(e) a terminal mounted on the outer surface of said closure, and

(1?) means electrically connecting said terminal to one of said contacts,

(g) said closure being rotatable relative to said housing to calibrate said switch.

8. A heat-responsive electrical switch comprising (a) a housing made of an electrically conductive material,

(b) an insulating closure mounted on said housing to close one end of said housing,

(c) a pair of electrically-conductive contact members secured on the inside face of said closure, both said contact members being arranged along spirals and extending spirally about a common center and being uniformly spaced apart from end to end,

(d) a bimetallic, heat-responsive element secured at one end within said housing and electrically connected thereto and having its other end disposed for movement between said contact members,

(e) a pair of terminals mounted on the outer surface of said closure,

(f) means electrically connecting the two terminals,

respectively, to said two contact members,

(g) said closure being rotatable relative to said housing to calibrate said switch, and

(h) means for securing said closure in any position to which it is rotated.

No references cited.

BERNARD A. GILHEANY, Primary Examiner. 

1. A HEAT RESPONSIVE ELECTRICAL SWITCH COMPRISING (A) A HOUSING OF AN ELECTRICALLY CONDUCTIVE MATERIAL, (B) AN INSULATING MEMBER CLOSING ONE END OF SAID HOUSING, (C) A SWITCH CONTACT FIXED TO SAID MEMBER ON THE INWARDLY FACING SIDE THEREOF, SAID CONTACT HAVING A CONTACT SURFACE LYING ALONG A SPIRAL AROUND THE CENTER OF SAID MEMBER IN A PLANE TRANSVERSE TO THE LENGTH OF SAID HOUSING, AND (D) A HEAT RESPONSIVE CONDUCTIVE ELEMENT MOUNTED WITHIN SAID HOUSING AND ELECTRICALLY CONNECTED THERETO FOR ELECTRICALLY CONNECTING SAID HOUSING TO SAID SWITCH CONTACT DURING TIMES WHEN THE AMBIENT TEMPERATURE IS BEYOND A PREDETERMINED VALUE, (E) SAID INSULATING MEMBER BEING ROTATABLE RELATIVE TO SAID HOUSING AFTER THE SWITCH IS ASSEMBLED THEREBY TO FACILITATE RAPID CALIBRATION OF THE SWITCH. 